This invention relates to the transformer art and it has particular relationship to power transformers and the mounting of the coils and cores of power transformers, i.e., to their coil-core assemblies. The standard American National Standards Institute ratings of the transformers with which this invention primarily concerns itself in kilo-volt-amperes are 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000 and 2500. There are also non-standard ratings of 30 and 45 KVA. While this application emphasizes power transformers in the interest of dealing concretely with this invention, it is to be understood that, to the extent that the principles of this invention may be adapted to transformers of other types, such adaptation is within the scope of equivalents thereof, typically as scope of equivalents is defined and explained in the interpretation of the Doctrine of Equivalents in Uniroyal v. Rudkin-Wiley, 5 USPQ 2d 1434 (CAFC 1988)(at 1443).
A coil-core assembly includes coil means, typically a plurality of coils each including a primary and a secondary and core means, typically rectangular cores each in the shape of a window linked to each coil. The assembly also includes a U-frame in which the coils and cores are mounted. The U-frame is composed of a cross member from whose ends legs extend. The coils and cores are mounted on the cross member of the frame and engaged firmly by the legs. In constructing the coil-core assembly, it is necessary to position the coils and cores within the U-frame and this involves manipulating the legs so that the coils and cores may be positioned within the frame. Since the U-frame is typically composed of channels of substantial thickness, typically steel 0.25-inch thick, or greater, the assembly of coils and cores in the frame presents serious obstacles and, in accordance with the teachings of the prior art, requires clamping and jacking devices.
Another factor requiring consideration is a consequence of the high power which the coil-core assembly converts. On the occurrence of an overload, such as a short circuit, within the coil-core assembly, large forces are developed which tend to blow the assembly apart. It is necessary that these forces be contained and for this purpose it has been the practice of the prior art to provide the frame with braces enhancing the complexity and cost of construction and the cost of the coil-core assembly itself.
In particular the braces are necessary where the U-frame is formed from a blank in which V notches are stamped in the regions where the legs are to be bent at right angles to the cross member. After the bending operation, there are slits at the joints between the legs and the cross member. In the event of an overload, the legs could be pivoted outwardly at the joints. In accordance with the teachings of the prior art, the legs are braced by heavy braces against the tank in which a prior-art coil-core assembly is installed.
It is an object of this invention to overcome the drawbacks and the deficiencies of the prior art, and to provide a coil-core assembly for a transformer lending itself to ready construction without clamping and jacking devices and which, when constructed, shall be effectively resistant to the forces produced by overloads such as short circuits. It is also an object of this invention to provide a method for producing such a coil-core assembly.